MRI suites have a control room with MRI Scanner operating components such as an RF amplifier and control cabinet (typically called the control room) and a separate room or chamber holding a high field magnet in which a patient is placed for an MRI procedure (typically called the Scanner room). MRI suites are enclosed in a Faraday shield (e.g., RF shielding) in order to electrically isolate sensitive MRI radio receivers and prevent them from picking up RF signals other than those emitted by the patient under examination. An RF-shielded wall separates the two rooms. A removable portion of the RF-shielded wall is typically called the penetration panel. RF shielding is important because it isolates the MRI scanner from external RF sources that can cause artifacts in the MRI image. For a typical MRI scanner chamber, the RF shielding causes at least 100 dB of signal attenuation of signals in the frequency range of 1 Hz to 150 MHz. Holes or openings made in this shielding can compromise the shielding effectiveness.
In most MRI suites, a grounded tubular waveguide provides the only access space for non-metallic cables, tubes, water or gas lines, and the like between the control room and the Scanner room. All other electrical cables have feed-through filters that are built on the penetration panel which is electrically connected to the Faraday shield. The waveguide is a circular pipe made of copper or brass that extends out a distance on each side of the penetration panel.
Waveguide depth and diameter is based on the fact that an electromagnetic field attenuates rapidly down a small diameter hole of sufficient depth, providing certain conditions are met. Thus, the diameter and length of the waveguide are chosen to inhibit or prevent RF waves from passing through it. Using the waveguide in this manner is commonly called “waveguide below cutoff”. This guideline allows small diameter holes to be made in conductive enclosures, as may be needed for ventilation, or as a pass-through for non-metallic members. Shielding effectiveness of an MRI suite can be compromised by inserting metallic components like cable through the waveguide or by using unfiltered or improperly filtered electrical connections.
MRI-guided interventional surgeries can require many types of electrical leads to operate properly. For example, as described in U.S. patent application Ser. No. 12/236,854, entitled MRI Surgical Systems For Real-Time Visualizations Using MRI Image Data And Predefined Data Of Surgical Tools (which describes components of, inter alia, a neurosurgery system also known as the CLEARPOINT® interventional system from MRI Interventions, Inc., Memphis, Tenn.) surgical systems can have connections or leads for MRI compatible cameras, data cable, mouse or trackball lead, monitor leads, video display monitors and/or other electrical inputs that require RF filters. U.S. patent application Ser. No. 12/237,033 describes MRI interventional systems with video cameras. See also, U.S. patent application Ser. No. 12/796,017, filed Jun. 8, 2012, entitled MRI-Guided Interventional Systems That Can Track And Generate Dynamic Visualizations Of Flexible Intrabody Devices In Near Real Time (which also describes components of, inter alia, a cardiac system also known as the CLEARTRACE® interventional system from MM Interventions, Inc., Memphis, Tenn.). In the past, relatively large “custom” openings were cut into penetration panels to support the required cabling for the intervention system. Removable filter boxes have also been used to help avoid permanent modification to MRI suites, see, e.g., co-assigned PCT/US2012/037334. The contents of the patent applications cited above are hereby incorporated by reference as if recited in their entirety herein.